Ion implantation systems are widely used in semiconductor processing to diffuse or implant positive ions onto regions of a semiconductor workpiece. Typically, an ion source generates an ion beam that is used to implant the semiconductor workpiece. The ion source typically comprises an indirectly heated cathode assembly having a filament for heating the cathode.
A conventional ion source having an indirectly-heated cathode typically comprises an arc chamber (also called a plasma chamber), cathode assembly, filament, insulator block, graphite support plate, and a filament clamp assembly, wherein the filament is positioned within a cavity defined by the cathode. The cathode is heated by an electron bombardment from the filament, whereby the cathode emits electrons thermionically within the arc chamber. Assembly and position of the filament with respect to the cathode directly relates to performance, efficiency, and life expectancy of the ion source.
A typical filament employed in an ion implantation system cathode assembly comprises two leads with a filament loop extending between the leads. The leads are typically individually held in place by respective filament clamps, whereby clamping jaws of the filament clamp are tightened around the leads via a pair of screws threaded into a hole in the respective filament clamp. Due, at least in part, to the extreme high temperatures in the ion source, material from the filament can deposit on the threads of the screws, thus making the threading of the screws into the holes difficult. Similarly, galling of the threads can occur, which can lead to welding together of the threads, thus losing the ability to tighten or loosen the clamp to the leads. Further, the high temperatures involved in the ion source can lead to stresses within the cold-formed screws to relax, thus further worsening the ability to adequately clamp the filament leads and provide proper electrical connection thereto. When the electrical connection to the filament is compromised or the filament clamps can no longer perform adequately, repair or replacement of the clamps is typically necessary, thus resulting in increased maintenance costs and downtime for the ion implantation system.